Google Collections Library

Google Collections Library is the extension of Java 1.5 Collection Framework. As we all know the collection framework is mostly used to handle objects in the Java Programming. So I think an extension API to this Its a very interesting as well as useful development to the Java world. Now Google is released its ALPHA version. This API includes so many new types, utility classes and some other helper implementations.The major new types are:

BiMap. A Map that guarantees unique values, and supports an inverse view.

Multiset. A Collection that may contain duplicate values like a List, yet has order-independent equality like a Set. Often used to represent a histogram.

Multimap. Similar to Map, but may contain duplicate keys. Has subtypes SetMultimap and ListMultimap providing more specific behavior.